The present invention relates generally to vehicle wheel alignment measurement procedures, and in particular, to a method for measuring and compensating steering-angle sensitive wheel alignment angle and distance measurements for the effects of altering a vehicle wheel steering-angle or distance during a vehicle wheel alignment adjustment procedure.
During a vehicle wheel alignment process, the operator is occasionally required to carry out steered-wheel alignment angle adjustments for wheel alignment angles measured with the vehicle steered in the straight-ahead direction. For example, measured camber and caster angles vary in relationship to the current steering-angle (toe angle) measurement. To further complicate matters, the caster angle of a steerable wheel is difficult to measure. Caster is defined as an angle between a vertical axis and a projection of an invisible steering axis onto a vertical plane containing the thrust line of the vehicle. Hence, a representative measurement, referred to as “live caster” KLive is either acquired from a caster transducer on a locked wheel alignment angle sensor secured to a steered vehicle wheel, or from the caster value for a fixed position of a wheel alignment measurement system optical target secured to a steered vehicle wheel after a measured caster angle (K) for the wheel has been calculated from measurements taken by alignment sensors.
The measurements required to calculate the measured caster angle are obtained during a caster steer procedure, and are based on either changes in the camber angle of the wheel or, for machine-vision based alignment systems utilizing the Schur method of calculating caster, on a minimum of 2 different images of the wheel or target as the toe angle of the wheel changes. Specification values for camber and caster angles are typically defined only for a specific steering-angle (toe angle), such as 0° toe, or with the steering-angle (toe angle) aligned relative to the vehicle thrust line.
Often it is difficult or awkward for the operator to maintain the vehicle steering in a specified location and access the various suspension components and adjustment points required to complete the necessary alterations. Additionally, during a vehicle wheel alignment adjustment procedure, any steering angle changes are typically made by turning the vehicle steering wheel from the driver's seat position, and not by turning the vehicle wheels directly, resulting in lost time to complete the alignment adjustment procedure, additional physical effort, and an inconvenience to the alignment technician who is required to climb in and out of the vehicle.
For some wheel alignment angle adjustments, the operator is required to initially steer the vehicle wheels to a straight ahead position, or to another selected position, from the driver's seat, make the necessary adjustments causing the steered location of the vehicle wheels to change, and then return to the driver's seat to steer the wheels back to the selected position to continue making adjustments of the alignment angles. This time consuming process is repeated several times until the adjustments of the alignment angles results in the alignment angles being within specification while the vehicle is steered to the selected position.
Furthermore, when the operator turns the steered wheel from the straight-ahead or selected position, the measured value for the steering-angle sensitive alignment angle, such as camber or live caster, will change in relationship to the steered angle of the vehicle wheel. If the operator attempts to adjust the steering-angle sensitive alignment angle with the wheel steered away from the straight ahead or selected position, using the measured value associated with the straight-ahead or selected steered position, the resulting adjustment will be incorrect when the wheel is returned to the straight-ahead or selected steered position.
Accordingly, it would be advantageous to provide a method for compensating steered-angle sensitive wheel alignment angle measurements for the effects of steering a wheel away from a straight ahead or selected measurement position, thereby enabling an operator to carry out a vehicle wheel alignment angle adjustment without having to maintain a wheel in a straight-ahead or other selected steered condition during an alignment angle adjustment, or requiring the operator to continually return the wheel to the straight-ahead or selected position to acquire updated measurements of an alignment angle during the adjustment thereof.
Furthermore, when the operator turns the steered wheel to a straight-ahead position relative to a vehicle thrust-line, there may be some measurements such as the levelness of the sensors which may not match a previous value of the same measurement within a given tolerance because the previous value was acquired when the steered wheel was aligned relative to the vehicle's center-line.
Accordingly, it would be advantageous to provide a method for compensating steered-angle vehicle measurements acquired at a non-optimal steering angle for deviations associated with the non-optimal steering angle. Doing so allows an operator to perform fewer steps during a vehicle measurement or adjustment procedure.
Furthermore, when the operator turns the steered wheel from the straight-ahead or selected position, a measured value for a steering-angle sensitive alignment distance, such as setback or wheelbase on the vehicle's left and right side, will change in relationship to the steered angle of the vehicle wheel. If the operator attempts to adjust or measure the steering-angle sensitive alignment distance with the wheel steered away from the straight ahead or a selected position, the results are likely to be incorrect.
Accordingly, it would be advantageous to provide a method for compensating steered-angle sensitive wheel alignment distance measurements for the effects of steering a wheel from a straight ahead or selected measurement position. This would enable an operator to carry out a vehicle wheel alignment distance adjustment or measurement without having to maintain a wheel in a straight-ahead or other selected steered condition. The operator would no longer be required to continually return the wheel to the straight-ahead or selected position to acquire updated measurements of an alignment distance currently being adjusted.
During vehicle wheel alignment procedures, it is often necessary for an operator to “lock” the vehicle brakes to ensure that the wheels of the vehicle do not roll during an alignment angle adjustment or measurement procedure. For example, it is particularly important that the steered wheels of a vehicle be prevented from rolling movement during a procedure where the steering axis inclination angle measurement is calculated which requires steering the vehicle wheels from one side to another.
One method commonly utilized to confirm an operator has “locked” the vehicle brakes when carrying out a procedure where the wheels are steered involves comparing a measurement of the live caster angle obtained when the steered vehicle wheel is in the straight-ahead position with measurements of the live caster angle obtained when the steered vehicle wheel is turned either to the left or right by a predetermined amount. If the compared measurements differ by more than a predetermined value, the vehicle brakes are assumed to be “locked”. While this method works for most vehicles, it is well known that different vehicle makes and models have different live caster angle difference thresholds from the straight-ahead position to a turned position, and accordingly, the predetermined value utilized for one vehicle may not be applicable to another vehicle.
Accordingly, it would be advantageous to provide a method for adapting a live caster angle difference threshold for each different vehicle to detect if the vehicle brakes are in a “locked” configuration, and to provide a method for detecting if the vehicle brakes are in a “locked” configuration which does not rely on comparison with a database of predetermined or fixed values.
During vehicle wheel alignment procedures, it is occasionally necessary for an operator to steer the vehicle wheels in order to access a suspension component or an alignment angle adjustment location such as a tie rod for adjusting toe angle. However, alignment angle measurements such as toe angle measurements are typically specified with the vehicle wheels steered straight ahead relative to a thrust line of the vehicle. Alternatively, alignment angle measurements such as setback angle are typically specified with the vehicle wheels steered straight ahead relative to a center line of the vehicle. Steering of the wheels to access the alignment angle adjustment location or suspension component alters the steering wheel angle from a centered position in which the front vehicle wheels are steered straight ahead relative to the thrust line or center line.
Accordingly, it would be advantageous to provide a method for determining the toe angle value for a steered wheel at a preferred steering orientation, such as steered-ahead relative to the vehicle thrust line, independent of the current steered wheel steering orientation to improve alignment angle adjustment procedures.
During a caster angle measurement procedure it is conventional for a steered wheel of the vehicle to be steered to either the left or right at 10° +/− a predetermined tolerance, or at 20° +/− a predetermined tolerance. Caster angle measurements acquired with the wheel steered short of, or beyond, the 10° or 20° target positions may not correspond with the predetermined caster angle specification values established for the 10° or 20° target positions due to the effect of the steering-angle.
Accordingly, it would be advantageous to provide a method for compensating measured caster angle values for the effect of steering-angle deviations, such that meaningful comparisons with predetermined caster angle specification values established for the 10° or 20° target positions may be made.
During a caster angle measurement procedure it is conventional for a steered wheel of the vehicle to be steered to either the left or right to a predetermined steering-angle. As the steered wheel of the vehicle is steered, the ride height of the vehicle changes. Some OEM alignment specifications are associated with a particular ride height at a predetermined steering-angle before being valid.
Accordingly, it would be advantageous to know how the ride height changes as the vehicle is steered such that meaningful comparisons can be made in alignment angles at all steering-angle deviations.